Levels of Specific Nutrients in Sugar Beet Factory Spent Lime and Their Impact

Spent lime is a by-product of the sugar beet sugar purification process. It is generated by heating mined calcium carbon limestone to form calcium oxide and carbon dioxide. These two products are injected into the thick juice (from the sugar beet processing) and reforms calcium carbonate. When the calcium carbonate reforms it captures or adsorbs many of the impurities in the juice and precipitates from the juice. The precipitate forms a solid lime product that needs to be discarded leaving behind the thin juice from which sugar is extracted. The seven sugar beet processing factories in North Dakota and Minnesota produce approximately 500,000 tons (dry weight basis) of spent lime annually. Historically, spent lime has simply been stock piled on site at each of the factories. As a result, large mounds of this material are present at each factory site and the mounds continue to grow each year. Storage of spent lime in this manner may create problems in the future for the factories as current storage permits expire, stock piles grow larger and environmental and space limitation awareness increases. One, potential disposal possibility is to apply it to the land or production fields. Spent lime is sold as Lime X in Europe and farmers apply it to their fields. However, these fields tend to have low soil pH and liming is required as a general management practice. Generally, spent lime has about 86% of the acid neutralizing potential as an equivalent quantity of fresh lime. Most soil pH in eastern North Dakota and western and central Minnesota is naturally at alkaline levels. There are isolated areas were soil pH may be acidic and require lime application as part of the management practice. But, many of the soils in the sugar beet factory areas are already at pH levels of 7.5 or above and do not require lime. There is little need to use spent lime from the sugar industry to correct soil pH problems. In isolated areas near the Minn-Dak Sugar Cooperative, a few growers were concerned about carryover of herbicide that was applied the previous year. The soil in these areas tended to be slightly acidic, which can contribute to herbicide carryover issues. Spent lime from the local sugar processing factory was applied in an attempt to raise soil pH and accelerate the break down, thus reducing the carryover, of the herbicide. Research was also initiated at NDSU to study this potential effect of spent lime. Interestingly, it was observed that Aphanomyces root rot was lessened where spent lime was applied in these experiments. One grower applied spent lime to approximately five acres in 1997 in an attempt to reduce herbicide carry over. When sugar beet was grown in 2003, the entire field had a severe infestation of Aphanomyces root rot except the area that received spent lime 7 years previously. Aphanomyces root rot in sugar beet is becoming a larger problem in the sugar beet growing areas of North Dakota and Minnesota. There is no effective control of this disease except for developing variety resistance. The possibility of using a factory produced by-product that is becoming troublesome to deal with, but may have a positive impact on this disease, is exciting. Thus, experiments were initiated to examine this potential (See Windels et al., in this volume for details of the disease aspect of the experiment). Since spent lime is formed during sugar processing and its purpose is to remove impurities from the juice, it seems possible that it may contain numerous chemical components, some of which may be considered nutrients. Factory chemical analysis of spent lime verify that it contains many potential nutrients such as phosphorus (P), nitrogen (N), and other micro and macro nutrients in addition to organic compounds. Exactly what chemical form these potential nutrients exist as in the spent lime and if they can indeed be utilized as crop nutrients is not known. It also seems logical that the impurities removed from the juice when spent lime is formed may differ with juice made from sugar beet grown in different regions on different soils in different environments. Therefore, the impurities in the spent lime may also vary among the factories.